1. Field of the Invention
The present invention is directed to a current limiting circuit interrupter, and more particularly to a current limiting circuit interrupter with magnetic arc driving means.
2. Description of the Prior Art
Circuit interrupters with magnetic arc driving means are well known in the art for effecting rapid current limiting action by magnetically blowing out or elongating the arc formed between the arcing contacts upon passage of overcurrents in excess of the rated current of the circuit. One form of the arc driving means effective for magnetically elongating the arc is to provide one or more magnetic windings in the vicinity of the arcing contacts for producing lines of magnetic force which act on the arc to magnetically drive it for elongation thereof. Although the magnetic windings are preferred for a rapid arc extinction purpose from the viewpoint that the arc at its instance of formation can be rapidly driven by the external magnetic field produced by the windings rather than the magnetic field to be produced by the arc current itself, there is certain limitation to the size of the windings for maintaining the heat loss thereof at a minimum in addition to increasing the intensity of the magnetic force to be applied to the arc for effective arc driving. In this sense, small-sized magnetic windings are preferred to be disposed in close relation to the arcing contacts in order to concentrate its lines of magnetic force to the arc for effective and rapid magnetic drive thereof. However, with the utilization of small-sized windings, there arises another problem that the entire arc path or the contact separation distance cannot be laid under the influence of the desired magnetic field generated by the windings to drive the arc in one direction. In other words, when the windings are disposed around the contacts in an attempt to concentrate its internal lines of magnetic force passing inside of the windings to the arc for driving it in one direction, this magnetic drive effect would be only available for the initial contact separation where the arc path is totally under the influence of such internal lines of magnetic force. Once the contact separation proceeds to a stage where the arc path or contact separation distance is extended to go out of the region under the influence of the internal lines of magnetic force, the portion of the arc outside of that region would be certainly subjected to the external lines of magnetic force which pass outside of the windings to transverse the arc path in the opposite direction to the internal lines of magnetic force and is therefore driven thereby in the opposite direction, adversely affecting the arc elongation.